This invention relates to a medical apparatus, and more particularly, to a needle assembly for conducting biological fluids to and from a patient.
In medically treating a patient, it is sometimes necessary (1) to introduce fluids, such as intravenous solutions, blood, etc., into the patient's body, or (2) to remove fluids from the patient. This may be accomplished by employing a needle assembly which is sometimes referred to as a fistula set. Such assemblies include a hollow metal needle for insertion into a vein or artery and an appropriate conduit connected to the other end of the needle through which the fluid can flow to or from the patient.
The needle is made from small diameter hollow stainless steel tubing, one end of which has been ground to provide a beveled edge for insertion into a vein or artery. The conduit is normally a larger tube made of medical grade polyvinylchloride which has an inside diameter substantially larger than the outside diameter of the steel tubing.
The conduit must be sealed to the needle so as to avoid any leakage of fluid at that junction. One method for sealing such needle assemblies has been to employ spacer members which are solvent sealed to each other and to the conduit using cyclohexanone. In one particular assembly, a thin layer of adhesive is bonded to the periphery of the needle at the butt end (i.e., the end opposite the beveled end) and then a vinyl sleeve is shrink-fitted about the adhesive. The adhesive bonds to the steel tube and provides a roughened surface for establishing a mechanical bond between the sleeve and the adhesive. A spacer or collar is then fitted about the sleeve. The collar has an outside diameter normally sufficient to engage the inside diameter of the conduit. The sleeve, collar and conduit have been solvent sealed to one another so as to provide a leak-free junction.
It has been found to be desirable to provide a more reliable junction between the needle and conduit than has been available by solvent sealing, but without changing the physical structure of the fistula set.
In addition to solvent sealing, there exists other sealing techniques, such as mechanical or radio frequency (RF) heat sealing. Mechanical sealing would require application of a binding member about the outside diameter of the conduit so as to mechanically hold the conduit, spacer, sleeve and needle together and was felt to be undesirable from a manufacturing point of view. RF heat sealing of plastic conduits is known and normally requires the use of (1) a removable solid brass or other highly electrically conductive metal mandrel as one electrode which is inserted into the conduit and (2) an external electrode applied around the outside of the conduit. Due to the small inside diameter of the needle, it was known that such a mandrel would be difficult to insert for heat sealing purposes. Furthermore, due to the hollow shape of the needle and that it was made of stainless steel rather than brass, it was not believed that RF heat sealing of the junction could be effected reliably in an isolated location using the needle as a mandrel.
It is therefore another object of this invention to provide an appropriate method for sealing the needle assembly.
These and other objects of the invention will become apparent from the following description and appended claims.